Modern cookware is often coated with non-stick material to release food quickly and easily, making serving and clean-up less troublesome. Coating metal cookware has been relatively successful where multi-layered coating techniques have been used to improve the bond between the cooking surface and the non-stick coating.
Applying non-stick coatings to ceramic cookware has proven more difficult. The ceramic substrate of conventional ceramic cookware is usually glazed to seal the otherwise porous surfaces, but the glazing does not have the characteristics needed to provide the required non-stick surfaces. The glazing commonly hinders or prevents the application of non-stick coatings to the cooking surfaces. As such, food typically becomes baked onto conventional ceramic cookware, making serving and clean-up difficult. While ceramic cookware with a reliable and long-lasting non-stick coating would be extremely useful, it is currently unavailable on ceramic cookware such as baking dishes, casserole dishes, slow-cookers, etc.
Another problem with applying non-stick coatings to ceramic cookware is the temperature gradients common in the ceramic substrate during cooking or baking. The temperature gradients that exist near the heat source and between the surface of the food and the air provide a harsh environment that tends to degrade and break down non-stick coatings. These temperature gradients add to the above-described difficulty in bonding the non-stick coating to the glazed surfaces and further increase the difficulty of producing ceramic cookware with a reliable non-stick coating.
Different types of ceramic cookware experience different cooking conditions that directly affect the intensity of the temperature gradients. Ceramic cooking appliances such as slow-cookers typically experience more extreme temperature gradients than baking dishes or casserole dishes due in part to the type and location of the heat source and the long cook times associated with slow-cooker applications. Unlike baking or casserole dishes used in the microwave or conventional oven for relatively short cook times, slow-cookers have heating elements in direct or near-direct contact with the ceramic cooking vessel, thereby generating localized and longer-lasting intense heat that creates sharper temperature gradients over the cooking vessel. Also, slow-cookers are often exposed to cool ambient temperatures at the food/air interface. As it is being cooked, the hot food is in contact with a portion of the ceramic cooking vessel while ambient air contacts the vessel just above the surface of the food. This interface experiences another temperature gradient that can be sharper than those associated with baking or casserole dishes used in warmer environments such as ovens or microwaves. As any slow-cooker user knows, it is these areas (the area adjacent the heating element and the interface between the top of the food and the air), that experience the most stuck-on, baked-on and caked-on food remains.
In addition to harsher cooking applications, ceramic slow-cookers are also more difficult to clean than common ceramic cookware. Even assuming that the ceramic cooking vessel of a slow-cooker is removable, it is typically bulky and burdensome to clean. It likely does not fit in a dishwasher and often does not even fit in the sink. If the ceramic cooking vessel is not removable from the slow-cooker housing, clean-up is further complicated as the cooking vessel cannot be submerged due to the electronics inside the housing. Maneuvering the slow-cooker to achieve proper cleaning is difficult and troublesome. This cleaning burden is greatly increased when food is baked on to the ceramic cooking vessel. The excessive scrubbing required to remove the stuck-on food is complicated by the bulky and unmanageable shape and size of the typical slow-cooker.
In light of the problems and limitations of the prior art described above, a need exists for ceramic cookware (and more preferably for a ceramic slow-cooker) that has a reliable and long-lasting non-stick coating that simplifies use and cleaning. Each preferred embodiment of the present invention achieves one or more of these results.